The desire to have movable ribbon cables and other assemblies of electrical conductors, optical conductors, or pneumatic conduits in industrial machinery lead to the development of flexible supports for the assemblies. Many of the supports have taken the form of so-called “cable tracks.” Cable tracks are made of a linear series of interlocking segments that partially surround and cradle a group of conductors or conduits. The interlocking segments often have surface features that interact to confine the range of motion of the cable tracks and the associated conductors or conduits in order to prevent excessive bending or kinking of the conductors or conduits. In some applications, the motion of a cable track ranges between a flattened configuration and a configuration that curves in only one direction. Cable tracks are limited in many applications by their bulky size, weight, large bend radius, mechanical vibration, power consumption, and rapid wear. In some applications, such as manufacturing in a clean room environment, wear of the cable track material often produces particulates that contaminate the work area or work product.
In an effort to reduce the size and weight of cable tracks, European Patent No. 528,141 to Elocab Sonderkabel GmbH & Co. teaches the incorporation of a cable track-like support element into a cable assembly. In the Elocab Sonderkabel assembly, the support element is made of a linear chain of interlocking segments with surface features that contact and limit the relative motion of adjacent segments. The support element is placed between two or more parallel electrical or optical conductors. An “enveloping casing” is extruded over the combination to form the finished cable assembly.
Although the size and weight of the cable track-like support element in the Elocab Sonderkabel assembly may be reduced from those of conventional cable tracks, many of the problems of conventional cable tracks remain with the Elocab Sonderkabel assembly. For example, movement between adjacent interlocking segments of the support element causes mechanical vibration to be generated in the support element as the support element is moved through an arc. As the support element is moved through an arc, the fixed pitches and radii of the interlocking segments often cause the support element to bounce or hop. This bouncing or hopping is commonly referred to as “cogging.” In the manufacture of semiconductors and other high precision devices, cogging can limit the speed and undermine the mechanical precision of machinery used to manufacture the devices. If cogging could be eliminated from a support member, the result would be a support member that operates in a smooth, quiet, and more precise manner.
Just as with conventional cable tracks, the support element in the Elocab Sonderkabel assembly suffers from wear between contact surfaces of the interlocking segments of the support elements. As the contact surfaces wear, the joints connecting the segments together loosen and allow the support element to sag. Once sagging occurs, the support element can buckle and cause the useful life of the support element to rapidly decrease. At high acceleration rates, sagging can cause the support element to buckle, further decreasing the useful life of the support element.
In addition to the problems the Elocab Sonderkabel assembly shares with conventional cable tracks, the operation of Elocab Sonderkabel assembly is further limited by the methods and materials used to construct the assembly. In the Elocab Sonderkabel assembly, the enveloping jacket is extruded over the support element and associated electrical conductors. The use of an extrusion method to form the enveloping jacket limits the types of materials that can be used to form the jacket. The types of materials that are suitable for extrusion of the enveloping jacket can reduce the flexibility, range of motion, and useful life of the assembly. These limitations become particularly apparent in applications requiring small bend radii, rapid and precise reciprocating motion of the assembly over long periods of time. These limitations are exacerbated when multiple assemblies are stacked on top of one another or when an assembly rubs against a surface.
As demand for high precision manufacturing, clean room environments, and other mechanically rigorous applications increases, conventional cable supports with interlocking segments will find increasingly fewer uses.
In view of the limitations of conventional cable supports there is a need for a lightweight support member having qualities including a high degree of flexibility, low mechanical noise, a small bend radius, low particle generation, and long service life. To achieve these and other goals, the support member would not use interlocking segments. Rather, the support member would be made of a length of flexible material with a series of non-interlocking motion-limiting elements attached to the flexible material. The support member would have a wide range of motion in one direction and essentially no range of motion in an opposite direction. The support member would be easy to manufacture and incorporate into an assembly of conductors or conduits. Such a supported cable assembly would be particularly useful with machines that perform rapid and precise mechanical movements over long periods of time. In manufacturing applications requiring a clean environment, the supported cable assembly could be provided with an external jacket that would generate very few particulates during use.